Methods and apparatus for surfacing spherical objects



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METHODS AND APPARATUS FOR SURFACING SPHERICAL OBJECTS Filed Jan. 2, 1964 H G. l

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j A TTOR/Vf) United States Patent 3,283,445 METHODS AND APPARATUS FOR SURFACING SPHERICAL OBJECTS Morton S. Lipkins, 3 Nemeth St., Malverne, N.Y. Filed Jan. 2, 1964, Ser. No. 335,315 11 Claims. (Cl. 51-73) The present invention relates to methods and apparatus for surfacing spherical objects, more specifically by lapping and polishing such objects. The invention is particularly applicable to surfacing hard materials such as glass, quartz, crystalline silicon, synthetic sapphire, metals, et cetera in making lenses, domes, and other articles having spherical surfaces.

An object of the invention resides in the provision of a novel method and apparatus for surfacing objects that is of particular advantage where the objects are of large spherical extent, approaching or even exceeding a hemisphere. As an example, the invention may be applied in lapping and polishing the inner and outer surfaces of spherical domes in a manner to establish and maintain sphericity with optical standards of precision. Pursuant to the present invention, small parts of spheres such as lenses may be lapped and polished. Each individual lens may be of small spherical extent, but in applying the invention many lenses are cemented to a support so as to present a composite spherical surface of large extent that is to be surfaced.

As will be seen in the detailed description that follows, the illustrative embodiments of the invention that are presently preferred for carrying out the foregoing and other objects includes upper and lower members having confronting spherical surfaces, one being a tool and the other being a support that carries one or more articles to be surfaced. The upper member is constrained to rotate about a substantially vertical axis and the lower member is constrained to rotate at about an inclined axis. The incline of the axis is adjustable, and it is either adjusted from time to time during the treatment of a particular object, or the incline of the axis is oscillated as the surfacing continues. In the preferred arrangement the tool is the upper member, and it is not driven but it is induced to rotate as a result of its contact with the work. The tool is restrained against lateral shift, but it is free to rock into full face-to-face contact with the confronting portion of the work and to apply its weight against the work while the work is rotated about its variably inclined The tool thus applies its weight symmetrically or nearly symmetrically, utilizing its surface with maximum effect and uniformity. The work is of large spherical extent, and it is rotated. The tool ordinarily used represents a much smaller part of a sphere than the work. The entire surface of the work is carried into rubbing engagement with the tool in the course of the operation.

The sphericity of the surface 'being lapped or polished can be controlled by periodically adjusting the incline of the rotational axis of the work. Alternatively, the angle of incline may be cyclically varied during the surfacing operation. In some instances, it may even be found advantageous to oscillate the axis of the work at a greater frequency than the rotation of the work.

The method and apparatus are highly effective in surfacing objects that represent a large part of a sphere, completing the treatment more easily and with excellent control as to maintaining sphericity and in a shorter time than has been needed heretofore in the surfacing of such objects. As applied to lenses of small spherical angle individually, many such lenses can be mounted on a support so as to represent a large spherical angle. Pursuant to the present invention, a much larger number of lenses can be surfaced at one time than heretofore.

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Previous methods have usually been limited to smaller numbers of lenses involving a smaller composite spherical angle of the mounted lenses.

The nature of the invention, and its further objects and novel features will be better appreciated from the following description of the preferred embodiments shown in the annexed drawings.

In the drawings:

FIGURE 1 is a front elevation, partly in section, of a presently preferred embodiment of certain features of the invention, in condition to receive the tool and work support shown in'FIGS. 3, 4, and 6;

FIGURE 2 is a fragmentary cross-section of the apparatus viewed from the line 2--2 in FIG. 1;

FIGURES 3 and 4 are fragmentary lateral views, partly in cross-section, illustrating the coaction of a tool and a workpiece in the apparatus of FIGS. 1 and 2;

FIGURE 5 is a fragmentary front elevation, partly in cross-section, of a modification of the apparatus in FIGS. 1-4, inclusive; and

FIGURE 6 is a lateral view, partly in cross-section, illustrating the coaction of the tool and the work in the embodiment of FIG. 5.

Referring now to FIGURES 1 and 2, base 10 has a pair of uprights 12 that carry a support 14. A bearing plate 16 is mounted for rotation about a horizontal axis in the bearing 18.

Arm 20 is carried on a pivot 22 supported by a block 24. A stud 26 extending downward from block 24 extends through a nut 28 that rests on the bottom of a slot 30 in support 14. A projection 32 extends from arm 20, projection 32 being provided for complemental engagement with the socket of a tool to be described in connection with FIGURES 3 and 4. The stud 26 and nut 28 provide for vertical adjustment of the projection 32 in relation to the horizontal axis of plate 16 for adjustment of the tool relative to the workpiece engaged by the tool.

A bracket 34 extends from plate 16. Bracket 34 is adjustably fixed to plate 16 by means of studs 36 which have respective heads received in an undercut slot 38 in plate 16, bracket 34 being clamped to plate 16 by nuts 40 on studs 36.

Bracket 34 support a motor 42 and a reduction-gearing unit 44. Bracket 34 also carries a bearing 46 containing a drive shaft 48. Pulley 50 carried by reduction-gearing unit 44 operates pulley 52 on shaft 48 through a belt 54.

The upper end of shaft 48 has a portion 48b that is threaded and is adapted to be secured to the support 56' for a convex workpiece W (FIG. 3) or to a support 56a of a workpiece W (FIG. 4) having a concave surface to be treated; and it will be appreciated that either workpiece, W or W, may be in the form of a matrix to which a large number of smaller workpieces w (FIG. 6) are united. The bearing 46 supports a combined shield and tray 53 for catching abrasive slurry that is at times used in the operation of the apparatus described.

On base 10 there is a reduction-gearing unit 68 coupled to a motor 62 that drives this gearing. Output shaft 64 of unit 60 carries a crank 66. A link 68 is connected by a pivot 70 to crank 66. The point at which rod 63 is connected to crank 66 is adjustable, as by means of a number of holes in crank 66 for receiving pivot 70. A rod 72 extends rigidly from bracket 34 and carries a pivot member 73. A bore in member 73 receives rod 68 slidably for adjusting the effective length of rod 63, and screw 73a fixes rod 68 in any adjusted position. Rotation of shaft 64 and crank 66 causes plate 34 and shaft 48 carried thereby to oscillate about the horizontal bearing aXis of plate 16.

Notably, the axis 43a of shaft 48 is at a slant angle in FIGURE 1, and this slant angle changes in dependence 3 on the position of crank 66 and on the adjustments at the ends of rod 68.

In the course of rotation of crank 66, the axis of shaft 48 moves between an extreme angle displaced from the vertical, and approaches a vertical position or even swings past the vertical. The angle through which shaft 48 swings depends on the adjustments at the ends of rod 68.

When support 56 (FIG. 3) is fixed to shaft 48, and a workpiece W is fixed to support 56 as by means of cement, the external spherical surface of workpiece W is presented to a tool 74. Tool 74 may take various forms, depending upon the nature of the operation to be carried out. For example, tool 74 may have a concave inner surface engaging workpiece W, where the tool surface is grooved and the tool is made of cast iron. As abrasive material in the form of slurry may be fed between the work and the tool in any suitable manner, as by applying the slurry to the surface of workpiece W where that workpiece extends outside the tool 74, or the slurry may be fed through a hole through tool 74. A socket of tool 74 that engages workpiece W is spherical and complemental to the workpiece, and the tool surface represents a large spherical angle which may approach but does not exceed a hemisphere in extent. The solid angle represented by workpiece W, on the other hand, may approach or exceed a hemisphere. The connection 36, 38, 40 between bracket 34 and plate 16 is advantageously adjusted so that the spherical center of the surface to be treated lies along the horizontal axis of bearing 18 about which bracket 34 oscillates. The level of pivot 22 may be adjusted so that the axis of symmetry of tool 74 is vertical and passes through the oscillatory axis of bearing 18.

In preparing for a lapping operation, a spherical workpiece W or W is cemented to to support 56 or 56a on the threaded end 48b of shaft 48, and a spherical tool 74 or 7411 that is at least nearly complemental to the shape of the workpiece is disposed on the workpiece. Projection 32 is received in socket 76. Using adjustments 26-28 and 3638-40 (as well as others that may be found desirable) the axis 761: of symmetry of the tool and the rotational axis 48a of the workpiece are caused to intersect at a point vertically below projection 76. In this way, the tool rests stably on the workpiece and its bearing force on the workpiece is distributed symmetrically about the vertical axis. The workpiece is rotated about its axis by drive means 42, 44, 48, 50, 52,, 54. The surface of tool 74 may be abrasive, and for example tool 74 may be of metal loaded with diamond particles. In a modified application, abrasive slurry is fed to the engaged surfaces of the tool and the workpiece. As the workpiece rotates, the tool is caused to rotate, but at a lower speed, so long as the axis of the work is inclined in relation to the tool axis; and as a result, the surface of the workpiece is lapped.

Accurate control of sphericity is achieved by varying the angle of incline of shaft 48. This is accomplished in either of two ways, either by indexing crank 66 from time to time during the rotation of shaft 48, or by rotating crank 66 continuously. Both techniques are useful in succession, in completing the lapping treatment quickly and in correcting for distortions that may exist initially and those that may occur as the treatment progresses. The oscillation of axis 48a may be made rapid and the rotation about axis 48a be relatively slow. Experience will show that each of these motions is useful in quickly lapping the nearly spherical surface of the workpiece to the desired smoothness, radius, and spherical uniformity. Thereafter, the same motions may be used in polishing the lapped surface, as with rouge and with a clothfaced tool such as that shown in FIG. 6.

Depending on the proportions of the tool and the workpiece, the range of oscillation of shaft 48 may be varied to advantage, by adjusting the length of rod 68 between pivots 70 and 73, and by adjusting the radial position of pivot 70 on crank 66. At its maximum angle of inclination, the shaft 48 will ordinarily cause the circular edge of the tool to be tangent to the circular edge of the work, although a somewhat greater angle of inclination is permissible as illustrated in FIG. 4.

The method and the apparatus described are useful in surfacing convex spherical objects W and concave .objects W. The method and apparatus are also used to special advantage where the spherical angle of the object is large so as to approach or even exceed a hemisphere. The method and apparatus are also of special merit where many objects w (FIG. 6) are to be lapped and/or polished in one operation. By virtue of the large spherical angle of the surface treatment, a relatively large number of lenses can be surfaced in one operation, a larger number than would be possible in surface-treating arrangements limited to smaller spherical angles. The treatment proceeds rapidly and with excellent control by virtue of the symmetry of pressure distribution of the tool, and the varied incline of the work (whether by successive adjustments or by continuous variation) provides control that helps the attendant to correct errors initially present and to maintain sphericity to a high degree of accuracy.

FIGURE 5 is a modification of the apparatus in FIG- URES 1 and 2, in providing a modified mechanism for oscillating the axis of plate 16, and for accordingly swinging the rotational axis of shaft 48 in a vertical plane. The

parts in FIGURE 5 which correspond to those in FIG- URES l and 2 bear primed numerals and in the interest of brevity their description is not repeated here. Rod 68',

which is operated by crank 66', carries a rack that meshes with a pinion 82 at the back of support plate 14, rack 80 being held in mesh with pinion 82 by a guide 84. Pinion 82 operates a shaft 86 that is rigidly fixed to plate 16'. The mechanism illustrated in FIGURE 1 provides for limited oscillation of the axis of shaft 48 between angular limits from a maximum slope toward the vertical axis (and to some limited extent across the vertical axis in some conditions of adjustment). The apparatus of FIG- URE 5 includes a modified form of oscillating mechanism that provides for a wider angle of oscillation of shaft 48. The oscillation of shaft 48 has a range that is as far to one side of the vertical as the other.

The tool shown in FIGURE 6 rests on a number of small workpieces w such as lenses which are united in a cement or matrix as of pitch on the work support 56'. In FIGURE 6, the surface of tool 74"has a cloth or felt covering 88, and is suitable for use with polishing agents such as rouge.

The foregoing description of the presently preferred but illustrative embodiments of the invention in its various aspects is evidently susceptible of modification and the novel features may be utilized in other analogous applications by those skilled in the art. Consequently, the invention should beconstrued broadly in accordance with its full spirit and scope.

What is claimed is:

1. The method of subjecting a spherical object to a surfacing treatment, comprising the steps of supporting the 1 ob ect for rotation about an axis that passes symmetrically through said object, resting an at least approximately complemental spherical tool .on said surface with surfacetreating material interposed, restraining the center of said tool against displacement from a vertical axis through the spherical center of said surface, oscillating said axis repeatedly across asignificantly inclined mean position about a horizontal axis that passes through said spherical center, and, concurrently, rotating said object about said axis.

2. The method set forth in claim 1, wherein said axis is oscillated many times during each rotation of the object about its axis.

3. The method set forth in claim 1, wherein the object is rotated many times during each oscillation of the axis of rotation.

4. The method of subjecting a spherical object to a surfacing treatment, comprising the steps of supporting the object for rotation about an axis that passes symmetrically through the object and driving said object about said axis, resting an at least approximately complemental spherical tool on said surface with surface-treating material interposed, the tool having the shape of "a spherical sector and having an object-treating surface over substantially the whole sector, the tool being induced to rotate by rotation of the object, and for the duration of the treatment maintaining the axis of rotation of the object at positions varying from one side to the other of a substantially inclined mean position.

5. Apparatus for surface-treating van object having a large-angle spherical surface, said apparatus including a tool having a spherical-sector work-treating surface, a spindle having a work support at the upper end thereof for supporting an object whose surface is to be treated, first drive means for rotating said spindle, means for cating said tool over the object while allowing free rotation about a vertical axis and free seating gravitationally on a spherical-surfaced object, means supporting said spindle for oscillation about a horizontal axis through the spherical center of the object, and second drive means for oscillating said spindle about said horizontal axis to opposite sides of a substantially inclined mean position.

6. Apparatus in accordance with claim 5 wherein the locating means includes means for arresting the center of the tool along a fixed vertical axis.

7. Apparatus in accordance with claim 5 wherein said first and second drive means are coordinated to effect plural oscillations of said spindle for each rotation thereof.

8. Apparatus in accordance with claim 5 wherein said first and second drive means are coordinated to effect plural rotations of said spindle for each oscillation thereof.

9. The method of subjecting a spherical object to a surfacing treatment wherein the object and a substantially complement-a1 spherical-sector surfacing tool are members held in contact with each other while being moved relative to each other about a common spherical center, in cluding the steps of supporting one of said members from below as a lower member for rotation about an axis through said common spherical center, resting the other or upper member on said lower member, and rotating one of said members about an axis through said commonspherical center and inducing rotation of the other member about an axis through said common spherical center, and for the duration of the treatment maintaining the axis of said lower member in positions varying to opposite sides of a substantially inclined mean position.

10. The method set forth in claim 9 wherein said axis of said lower member is oscillated about said mean position during the surfacing treatment.

11. Apparatus for surface-treating an object having a spherical surface with a complemental spherical surfacing tool, where said object and said tool are spherical members held in mutual contact one above the other and moved relative to each other about a common spherical center, said apparatus including a spindle having at the upper end thereof a support for the lower one of said members, means locating the upper member above the lower member While allowing free seating of the upper member on said lower member, means for rotating one of said members and thereby inducing rotation of the other of said members, and means for oscillating said spindle about a substantially inclined mean position.

References Cited by the Examiner UNITED STATES PATENTS 537,971 4/1895 Fuller 51-73 1,538,811 5/1925 Hill 5197 2,463,698 3/ 1949 Kline. 2,982,057 5/ 1961 Stanhope 5173 FOREIGN PATENTS 1,045,228 11/ 1953 France.

LESTER M. SWINGLE, Primary Examiner.

Akin 

11. APPARATUS FOR SURFACE-TREATING AN OBJECT HAVING A SPHERICAL SURFACE WITH A COMPLEMENTAL SPHERICAL SURFACING TOOL, WHERE SAID OBJECT AND SAID TOOL ARE SPHERICAL MEMBERS HELD IN MUTUAL CONTACT ONE ABOVE THE OTHER AND MOVED RELATIVE TO EACH OTHER ABOUT A COMMON SPHERICAL CENTER, SAID APPARATUS INCLUDING A SPLINDLE HAVING AT THE UPPER END THEREOF A SUPPORT FOR THE LOWER ONE OF SAID MEMBERS, MEANS LOCATING THE UPPER MEMBER ABOVE THE LOWER MEMBER WHILE ALLOWING FREE SEATING OF THE UPPER 